After cervical hemisection of the spinal cord, the ipsilateral hemidiaphragm becomes paralyzed. This hemidiaphragm recovers, however, in several mammalian species if the contralateral phrenic nerve is transected. Although the phrenicotomy paralyzes the denervated hemidiaphragm, it activates a latent crossed medullospinal pathway (crossed phrenic pathway) which restores function to the opposite hemidiaphragm paralyzed by spinal cord injury. The purpose of this research is to determine if recovery can be achieved in the entire diaphragm after spinal cord injury. Electromyographic recordings from the diaphragm will be utilized to determine if repeated use of synapses in the crossed phrenic pathway will allow the synapses to operate after function is restored to the interrupted phrenic nerve. The contralateral phrenic nerve will be temporarily interrupted after hemisection by anesthetics, crush, or transection. The proposed experiments will also determine if functional recovery in both hemidiaphragms can be achieved by transecting the dorsal roots of the phrenic nerve opposite the hemisection. Since some of the afferent fibers in the nerve have an inhibitory influence on the contralateral phrenic nucleus, their interruption may activate the latent crossed phrenic pathway. Surgical, electrophysiological, histochemical, and histological methods will be employed in this research.